The present invention relates to a B-staged sheet having a high relative permittivity, prepreg having a high relative permittivity, its production process and a printed wiring board using its copper-clad board as a condenser or the like. Particularly, a printed wiring board obtained by making a hole with a carbon dioxide gas laser is suitably used for a semiconductor chip-mounting, small-sized, light weight and novel printed wiring board, as a high-density and small-sized printed wiring board.
In recent years, a high-density multi-layered printed wiring board is used for an electrical equipment which is decreased in size, thickness and weight. When a layer having a high relative permittivity is provided as an inner or outer layer of the printed wiring board and the layer is used as a condenser, a packaging density can be improved. A layer having a high relative permittivity has been made as an inner layer, an outer layer or a substrate of a multi-layered board by a method disclosed in JP-A-55-57212, JP-A-61-136281, JP-A-61-167547, JP-A-62-19451 or JP-B-5-415, in which an inorganic powder having a high relative permittivity, such as barium titanate, is incorporated in an epoxy resin, a modified polyphenylene oxide resin or the like, a fiber substrate such as a glass fabric is impregnated with the resultant mixture, the mixture is dried to obtain prepregs, a plurality of the prepregs are stacked, copper foils are placed thereon as the outermost layers, and the resultant set is laminate-formed to produce a copper-clad laminate having a high relative permittivity. This glass-fabric-substrate copper-clad laminate has a thick glass fabric thickness as thick as at least 409 xcexcm. When a resin is attached thereto, therefore, the thickness becomes 60 xcexcm or more. It has been impossible to produce a glass-fabric-substrate copper-clad laminate having a thinner insulation layer. In addition, the inorganic filler has a heavy specific gravity so that when the inorganic filler is dispersed in a varnish, it settled down. Therefore, there is found no case in which a large amount of the inorganic filler is incorporated. Further, the glass-fabric-substrate copper-clad laminate has a glass fabric substrate, so that it is difficult to impregnate a glass fabric substrate with a resin composition containing the inorganic filler in a large amount as large as at least 80% by weight and it is also difficult to attach the resin composition in a large amount to the surface of a fabric. Further, cracks of the resin composition and unevenness are found, and it is impossible to produce a fine prepreg. Therefore, when prepreg is prepared, the amount of the inorganic filler in the resin composition is generally 70% by weight or less. A plurality of the so-obtained prepregs are stacked, copper foils are disposed as the outermost layers, and the resultant set is laminate-formed to prepare a copper-clad laminate having a high relative permittivity. In Examples disclosed in each of the above publications, there are obtained only glass-fabric-substrate copper-clad laminates having a relative permittivity of about 10 to 20. Therefore, it is impossible to form a condenser having a large capacitance, and it is difficult to use the above copper-clad laminate as a copper-clad board having a condenser function.
On the other hand, even a copper-clad laminate obtained by using a resin composition containing a general thermosetting resin and an inorganic powder having a high relative permittivity is fragile and is weak in copper foil adhesion strength, when the inorganic filler is incorporated in a large amount. Further, it is impossible to produce a copper-clad board having high heat-resistance and having a relative permittivity of 50 or more, still less 100 or more. As shown in JP-A-9-12742, a high relative-permittivity film obtained by mixing a thermosetting resin with an inorganic powder having a relative permittivity of at least 50 without using a glass fabric substrate has a high resin viscosity in order to form the mixture into a film. Therefore, the upper limit of the content of the inorganic filler is about 60% by weight. Consequently, an obtained copper-clad laminate comprising the above film has a small relative permittivity as small as about 10. There is not obtained a copper-clad laminate having a relative permittivity of at least 50.
It is an object of the present invention to provide a high relative-permittivity B-staged sheet which has a thin insulation layer thickness of, for example, 50 xcexcm or less and a large relative permittivity of at least 50 and which is processible like a general glass-fabric-substrate thermosetting resin prepreg, and a printed wiring board obtained by making a penetration hole and/or a blind via hole in a copper-clad board comprising the B-staged sheet.
It is another object of the present invention to provide a high-density printed wiring board including a copper-clad board comprising the above B-staged sheet which is suitable for making a hole having a small diameter with a carbon dioxide gas laser.
It is further another object of the present invention to provide a prepreg having a high relative permittivity in which a resin composition excellently adheres to a substrate even when the resin composition contains a thermosetting resin and at least 80% by weight of an inorganic filler, which is excellent in adhesion strength to a copper foil when a copper-clad laminate is prepared by using the prepreg, which has a large relative permittivity of at least 10, preferably at least 20, and which is processible like a general glass-fabric-substrate thermosetting resin prepreg, and a production process thereof.
It is still another object of the present invention to provide a printed wiring board using a copper-clad laminate comprising the above high relative-permittivity prepreg.
According to the present invention 1, there is provided a high relative-permittivity B-staged sheet obtained by incorporating an insulating inorganic filler having a relative permittivity of at least 500 at room temperature into a solvent-less resin component so as to have an insulating inorganic filler content of 80 to 99% by weight, preferably 85 to 95% by weight.
According to the present invention, there is also provided a high relative-permittivity B-staged sheet according to the above, wherein the solvent-less resin component contains, as an essential component, a resin composition obtained by incorporating 50 to 10,000 parts by weight of an epoxy resin (b) that is liquid at room temperature into 100 parts by weight of a monomer of a polyfunctional cyanate ester and/or a prepolymer of said cyanate ester (a) and incorporating 0.005 to 10 parts by weight of a heat-curing catalyst per 100 parts by weight of the total amount (a+b) of the monomer of the polyfunctional cyanate ester and/or the prepolymer of said cyanate ester and the epoxy resin.
According to the present invention, there is also provided a high relative-permittivity B-staged sheet according to the above, wherein the above insulating inorganic filler is a product which contains at least one ceramic selected from the group consisting of a barium titanate-containing ceramic, a lead titanate-containing ceramic, a calcium titanate-containing ceramic, a magnesium titanate-containing ceramic, a bismuth titanate-containing ceramic, a strontium titanate-containing ceramic and a lead zirconate-containing ceramic or which is obtained by sintering at least one ceramic selected from the above group and pulverizing the sintered ceramic.
According to the present invention, there is also provided a printed wiring board obtained by making a penetration hole and/or a blind via hole in a copper-clad board having the above B-staged sheet.
According to the present invention, there is also provided a printed wiring board, wherein when the via hole and/or the penetration hole is made in a double-side copper-clad board and its copper foils by direct irradiation with a carbon dioxide gas laser by means of the pulse oscillation of a carbon dioxide gas laser having an energy sufficient for removing the copper foils, the penetration hole and/or the blind via hole of the above printed wiring board are made by carrying out an oxidation treatment to form a metal oxide or a treatment with a chemical on one copper foil surface of the double-side copper-clad board or disposing, as an auxiliary material for making a hole, a layer of a resin composition containing 3 to 97% by volume of at least one powder selected from the group consisting of a carbon powder, metal powder, a metal compound powder having a melting point of at least 900xc2x0 C. and a bond energy of at least 300 KJ/mol, on the above copper foil surface, and then directly irradiating the treated copper foil surface or the auxiliary material with a carbon dioxide gas laser.
According to the present invention 2, there are also provided a high relative-permittivity prepreg which is obtained by sandwiching an inorganic substrate or an organic fiber fabric substrate between the above high relative permittivity B-staged sheets and integrating these and its production process.
According to the present invention, there is also provided a high relative-permittivity prepreg, wherein the above inorganic substrate is a glass fiber non-woven fabric having a thickness of 100 xcexcm or less and containing at least 90% by weight of a flat glass fiber of which the cross section is flat and in which a flatness rate, represented by the length/breadth of the cross section, is 3.1/1 to 5/1, the cross sectional area is 90 to 98% of the area of a rectangle circumscribing the glass fiber cross section, and a converted fiber diameter is 5 to 17 xcexcm.
According to the present invention, there is also provided a high relative-permittivity prepreg, wherein the above inorganic substrate is a ceramic fiber substrate having a relative permittivity of at least 50.
According to the present invention, there is also provided a high relative-permittivity prepreg, wherein the above organic fiber fabric substrate is an aromatic polyester fiber non-woven fabric.
According to the present invention 2, there is also provided a printed wiring board obtained by making a penetration hole and/or a blind via hole in a copper-clad board comprising the above high relative permittivity prepreg.